Vehicle emission control systems may be configured to store fuel vapors from fuel tank refueling and diurnal engine operations, and then purge the stored vapors during a subsequent engine operation. The fuel vapors may be stored in a fuel vapor canister coupled to the fuel tank which contains adsorbent material, such as activated carbon, capable of adsorbing hydrocarbon fuel vapor.
The fuel tank may be further coupled to a vapor recovery line (vapor recirculation line) which may also be coupled to the fuel vapor canister and the fuel filler neck. The vapor recovery line may be configured to circulate and/or hold a percentage of refueling vapors, thus limiting the rate of fuel vapor canister loading. Further, depending on the fuel dispenser, the fuel vapors within the vapor recovery line may be returned to the fuel dispenser, thus limiting the total fuel vapor stored within the fuel vapor canister for a given refueling event.
However, if the vapor recovery line becomes blocked, fuel vapor will not circulate through the vapor recovery line, and the canister loading rate (and total load) will increase. Unlike other blockages in the emissions control system, a blockage in the vapor recovery line may not necessarily result in pre-mature shutoff of the fuel dispenser, and may thus go undiagnosed. This may lead to an underestimation of canister load following refueling, which may in turn lead to an increase in bleed emissions if canister purge operations are not updated to accurately reflect the current canister load. While the fuel tank pressure during the refueling event can also be used to estimate the canister loading rate, the fuel tank pressure may not increase in accordance with a vapor recovery line blockage, and may thus not provide an accurate reflection of canister loading in the case of degradation.
Furthermore, in a case where the vapor recovery line is blocked or restricted, some areas of the fuel system and evaporative emissions system may become isolated from vacuum or positive pressure that is utilized to assess a presence or absence of undesired evaporative emissions stemming from the fuel system and evaporative emissions system. More specifically, if there is a restriction in the vapor recovery line, and fuel in the fuel tank is above a fuel tank spud valve, then a fuel filler system may go undiagnosed in a test where vacuum is communicated to the fuel system in order to determine the presence or absence of undesired evaporative emissions. If parts of the fuel system (e.g. fuel filler system) go undiagnosed, undesired evaporative emissions may increase.
Thus, the inventors herein have recognized the above issues, and have developed systems and methods to at least partially address them. In one example, a method is provided, comprising testing for undesired evaporative emissions from a fuel system and/or an evaporative emissions system in a first mode when a vapor recovery line, configured to circulate and/or hold a percentage of refueling vapors, is degraded as determined by a steady-state pressure in the vapor recovery line during a refueling event, and testing for the undesired evaporative emissions in a second mode when the vapor recovery line is not degraded. In one example, testing for undesired evaporative emissions from the fuel system and/or the evaporative emissions system in the first mode includes conducting the test responsive to a fuel level in a fuel tank of the vehicle below a threshold fuel level, and wherein testing for undesired evaporative emissions from the fuel system and/or the evaporative emissions system in the second mode includes conducting the test responsive to the fuel level in the fuel tank being either greater than, or less than, the threshold fuel level. For example, when the fuel level is greater than the threshold fuel level and the vapor recovery line is degraded, a portion of the fuel system is isolated from another portion of the fuel system. In one example, the portion of the fuel system that is isolated includes a fuel filler system of the fuel system. In this way, an entirety of the fuel system and evaporative emissions system may be tested for the presence or absence of undesired evaporative emissions, even under conditions where the vapor recovery line is degraded. By conducting a test for undesired evaporative emissions in the first mode when the recovery line is degraded, and conducting the test for undesired evaporative emissions in the second mode when the recovery line is not indicated to be degraded, undesired evaporative emissions may be reduced or avoided.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.